It is now well known to utilize a piece of low coercive force, high permeability magnetic material as an EAS marker. Such markers were perhaps first disclosed in the French Pat. No. 763,681, issued in 1934 to Pierre Arthur Picard. More recently, it has become relatively well known to construct such markers of elongated strips of high permeability material in order to enhance the production of very high order harmonics, thereby improving the reliability with which such markers can be distinguished over signals from other articles such as briefcase frames, umbrellas, etc. Preferably, such elongated strips, often referred to as "open-strip" markers, exhibit a ratio of length to square root of cross-sectional area in excess of about 250. Such uses are exemplarily set forth in U.S. Pat. Nos. 3,665,449, 3,790,945 and 3,747,086. As such elongated strips are generally detectable only when the interrogating field is aligned with the strips, it is known from such disclosures to provide for multi-directional response by providing multi-directional fields in the interrogation zone or by providing additional strips in an L, T or X configuration. In the '449 patent it is also suggested that the marker comprise "closely spaced but, physically separate ferromagnetic strip held in fixed geometric relation to each other on or within a nonmagnetic substrate (such as very fine wire filaments or ribbons within a piece of paper)".
Markers such as disclosed in the above patents have all enjoyed certain commercial success. However, the use of the markers has been restricted by the size, and still primarily elongated shape heretofore believed to be necessary. Where additional sensitivity or shorter length markers are desired, it is disclosed in U.S. Pat. No. 4,075,6l8 (Montean) to provide flux concentrating elements on each end of the elongated strips.
Typical EAS systems originally designed to be used with elongated "open-strip" type markers, are the Model WH-1000 and 1200 systems, marketed by Minnesota Mining and Manufacturing Company. Such systems produce within the interrogation zones magnetic fields alternating at about 10 kHz, and having minimum intensities at the center of the zone of approximately 1.2 oersteds (Oe) when the fields generated in coils on opposite sides of the zone are in an opposing configuration and of approximately 2.4 Oe when in an aiding configuration. The two field configurations thus facilitate detection of a uni-directionally responsive marker oriented parallel to either of two directions.